The study sheds light only on an association, as the researchers were unable to determine an actual cause-and-effect relationship between sipping artificially sweetened drinks and an increased risk for stroke and dementia. Therefore, some experts caution that the findings should be interpreted carefully.

No connection was found between those health risks and other sugary beverages, such as sugar-sweetened sodas, fruit juice and fruit drinks.

"We have little data on the health effects of diet drinks and this is problematic because diet drinks are popular amongst the general population," said Matthew Pase, a senior research fellow in the department of neurology at Boston University School of Medicine and lead author of the new study.

"More research is needed to study the health effects of diet drinks so that consumers can make informed choices concerning their health," he said.

The new study involved data on 2,888 adults older than 45 and 1,484 adults older than 60 from the town of Framingham, Massachusetts. The data came from the Framingham Heart Study, a project of the National Heart, Lung, and Blood Institute and Boston University.

In the older-than-45 group, the researchers measured for stroke and in the older-than-60 group, they measured for dementia.

"The sample sizes are different because we studied people of different ages," Pase said. "Dementia is rare in people under the age of 60 and so we focused only on those aged over 60 years for dementia. Similarly, stroke is rare in people aged under 45 and so we focused on people older than age 45 for stroke."

The researchers analyzed how many sugary beverages and artificially sweetened soft drinks each person in the two different age groups drank, at different time points, between 1991 and 2001. Then, they compared that with how many people suffered stroke or dementia over the next 10 years.

Compared to never drinking artificially sweetened soft drinks, those who drank one a day were almost three times as likely to have an ischemic stroke, caused by blocked blood vessels, the researchers found.

They also found that those who drank one a day were nearly three times as likely to be diagnosed with dementia.

Those who drank one to six artificially sweetened beverages a week were 2.6 times as likely to experience an ischemic stroke but were no more likely to develop dementia, Pase said.

"So, it was not surprising to see that diet soda intake was associated with stroke and dementia. I was surprised that sugary beverage intake was not associated with either the risks of stroke or dementia because sugary beverages are known to be unhealthy," Pase said.

In response, Lauren Kane, a spokeswoman for the American Beverage Association, issued a statement from the group that said low-calorie sweeteners found in beverages have been proven safe by worldwide government safety authorities.

"The FDA, World Health Organization, European Food Safety Authority and others have extensively reviewed low-calorie sweeteners and have all reached the same conclusion -- they are safe for consumption," the statement said.

"While we respect the mission of these organizations to help prevent conditions like stroke and dementia, the authors of this study acknowledge that their conclusions do not -- and cannot -- prove cause and effect. And according to the National Institutes of Health (NIH), many risk factors can increase an individual's likelihood of developing stroke and dementia including age, hypertension, diabetes and genetics. NIH does not mention zero calorie sweeteners as a risk factor," the statement said. "America's beverage companies support and encourage balanced lifestyles by providing people with a range of beverage choices — with and without calories and sugar — so they can choose the beverage that is right for them."

"This article provides further evidence though on artificially sweetened beverages and their possible effects on vascular health, including stroke and dementia," said Dr. Ralph Sacco, professor and chair of neurology at the University of Miami Miller School of Medicine, about the new study.

Sacco was a co-author of an editorial published alongside the study in the journal Stroke on Thursday.

"We believe the pathways of which artificially sweetened beverages would affect the brain are probably through vascular mechanisms," Sacco said.

"When the authors controlled for hypertension and diabetes and obesity the effects diminish, which implies that some of the effects of artificially sweetened beverages could still be going through a vascular pathway," he said about the new study. "Many strokes are caused by hardening of arteries; and the risk of dementia is also increased by the hardening of arteries in large and small vessels. So, I believe the mechanisms may be through vascular disease, though we can't prove it."

Heather Snyder, senior director of medical and scientific operations at the Alzheimer's Association, called the new study "a piece of a larger puzzle" when it comes to better understanding how your diet and behaviors impact your brain.

"It's actually really more of your overall diet and overall lifestyle that is linked to cardiovascular disease and diabetes risk, and we do know that heart disease and diabetes are linked to an increased risk of dementia," said Snyder, who was not involved in the new study.

"We know that sugary and artificially sweetened beverages are not great for us. This study adds strength to that, and also says they may not be great for your brain, specifically," she said. "There are alternatives -- things we can all do everyday to keep our brains and our bodies as healthy as we can as we age." Alternatives such as regular cardiovascular exercise that elevates heart rate and increases blood flow and doing puzzles and games to activate and challenge the mind. These are recommendations from the Alzheimer's Associations list of 10 lifestyle habits to reduce risk of cognitive decline.